Table of Contents
Advertisement
A-42 HP 9895A Disc Memory Command Set
Buffered Write
Type:
Purpose:
Description:
Disc Write Commands
Disc write.
The disc controller takes data transmitted on the HP-IB
and stores it in an internal buffer before writing it on the
disc. This buffering allows the host system to transmit
asynchronously from an arbitrarily slow rate to about 190K
bytes per second. The maximum HP-IB data rate is faster
than the data rate to the disc, thus less time is used to
transfer one sector over the HP-IB than
it
takes to write
that sector. During the remaining time the HP-IB is free to
be used by other devices on the bus.
Following reception of the Write command, parallel poll
response is disabled, status of the specified unit is checked
and the parallel poll response is re-enabled.
At this time the bus controller should send the receive data
secondary followed by up to one sector of data bytes. After
seeing the receive data secondary, the 9895A will disable
parallel poll response and begin placing data bytes in its
buffer. The 9895A will stop accepting bytes after:
1. It receives a byte tagged with an EOI,
2. It has accepted one sector.
NOTE
If less than one sector is sent, the sector will be filled with data in
the buffer from previous operations.
After the buffer has been accepted by the controller, the
current address is checked with the target address. If they
differ, a seek to the target cylinder is performed. This may
occur if the actuator has slipped or if an auto-increment to
the next cylinder is required.
If an HP format disc is being used, the 9895A attempts to
write the 256 bytes in the buffer to the target sector. If the
write completes successfully, the target address is in-
cremented by one sector. If the target sector cannot be
found or a D bit is encountered, the sector is not written
and the target track is not incremented.
If an IBM format disc is being used, only 128 bytes from
the buffer are written to the disc. If the write completes
successfully, the target address is incremented by one sec-
tor. If the target sector is not found, the sector is not written
and the target address not updated.
Advertisement
Table of Contents
